What is a subnet mask?

A subnet mask divides an IP address into network and host portions. A mask of 255.255.255.0 (/24) means the first 24 bits identify the network, and the last 8 bits identify individual hosts—allowing 254 usable addresses.

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation uses a slash followed by the number of network bits. For example, /24 means a 255.255.255.0 mask. It replaced the old Class A/B/C system in 1993.

Why do I lose 2 addresses in every subnet?

The first address is the network address (identifies the subnet) and the last is the broadcast address (sends to all hosts). Neither can be assigned to a device. A /24 has 256 addresses but only 254 usable hosts.

IP Subnet Calculator — CIDR, Subnet Mask, Host Range

Common Subnet Sizes

CIDR	Subnet Mask	Total IPs	Usable Hosts	Typical Use
/30	255.255.255.252	4	2	Point-to-point links
/28	255.255.255.240	16	14	Small office
/24	255.255.255.0	256	254	Standard LAN
/20	255.255.240.0	4,096	4,094	Medium campus
/16	255.255.0.0	65,536	65,534	Large enterprise
/8	255.0.0.0	16,777,216	16,777,214	Class A network

Private IP Ranges

Three ranges are reserved for private networks (RFC 1918):

Range	CIDR	Addresses
10.0.0.0 – 10.255.255.255	10.0.0.0/8	16.7 million
172.16.0.0 – 172.31.255.255	172.16.0.0/12	1 million
192.168.0.0 – 192.168.255.255	192.168.0.0/16	65,536

Subnetting Strategy

Size subnets to match actual need plus 20-30% growth. A team of 40 people doesn't need a /24 (254 hosts) — a /26 (62 hosts) leaves room for printers, APs, and future hires without wasting address space. VLANs combined with subnets keep broadcast domains small, reducing noise and improving security through segmentation.

How to Use This IP Subnet Calculator

Enter an IP address and subnet mask (CIDR notation or dotted decimal). The calculator shows the network address, broadcast address, usable host range, and number of hosts.

Formula & How It Works

Network Address = IP AND Subnet Mask. Broadcast = Network OR (NOT Mask). Usable Hosts = 2^(32 – CIDR) – 2. CIDR /24 = 256 addresses, 254 usable.

Calculation Example

192.168.1.50/24: Network = 192.168.1.0, Broadcast = 192.168.1.255, Usable range = .1 to .254, 254 hosts.

Expert Tips

The /24 subnet (255.255.255.0) is most common for small networks. Subnetting lets you divide large networks into smaller, more manageable segments. Always reserve addresses for the gateway and DHCP server.

IP Subnet Calculator

Common Subnet Sizes

Private IP Ranges

Subnetting Strategy

FAQ

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How to Use This IP Subnet Calculator

Formula & How It Works

Calculation Example

Expert Tips